What is "sound pressure"

n. the difference between the instantaneous pressure at a point in a sound field and the average pressure at that point [syn: instantaneous sound pressure]

Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average, or equilibrium) atmospheric pressure, caused by a sound wave. In air, sound pressure can be measured using a microphone, and in water with a hydrophone. The SI unit of sound pressure is the pascal (Pa).